Killed steel for pump components

[SENGUTTUVAN]

The specification for a pump impeller is given as Killed Carbon steel. Vendor is offering for 12% chrome steel ( ASTM A743 CA6NM) . It is argued that killed steels are only a process of deoxidising and he is giving a superior steel which is also a killed steel only.
The composition of the ASTM A743CA6NM indicates that the Carbon % is 0.06 ( max).
I would like to know the following:
Whether the vendor statement is correct and acceptable?
Whether Carbon % have anything to do with the decision of asking for a killed steel? Because it is said that if the Carbon is less than 0.35% those steels need not be killed.Is this statement is correct?

 

[BigInch]

High carbon steels when formed with dissolved oxygen can combine with carbon to form carbon monoxide bubbles. Bubbles = bad. Killed steel makes SiO2 or AlsO3 compounds instead of bubbles. No bubbles = good.

I don't know if A743 is better or not, but if its carbon content is less than 0.06%, it does not need to be killed. Killing is normally reserved for steels with C >= 0.25%.



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"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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[SJones]

CA6NM is a cast martensitic STAINLESS steel. Whether this substitution can be made depends upon what you are trying to pump.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[SENGUTTUVAN]

SJones

The pump is to be used in the Refinery plant to pump Hydrocarbon at 260Deg C. The Pump case material and the Impeller has been specified as Killed Carbon Steel and the Wear rings are specified as 12% cr steel. Vendor is proposing to give Impeller in 12% cr steel ( A743 CA6NM).

 

[svi]

CA6NM has 0.06% C max.

What may be the reasoning why killing (deoxidation of undesirable elements) is not required, if the C% is below a certain %?

Sajit

 

[EdStainless]

as a stainless it would be deoxidized. Not for the same reasons as in a carbon steel though. They get the carbon low by injecting oxygen into the molten metal and burning it out. They then use argon gas and some minor additions of Si or Ti to remove the remaining oxygen. Then they can make the final adjustment of the Cr levels.

If you like using 12% Cr wear rings then using solid 12% Cr impellers should not be a problem. Do they meet the same mechanical property (strength) requirements?

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